Methods for producing a printed wiring board are classified into two a tenting method and a plating method. In the tenting method, copper through holes for mounting a chip are protected by use of a resist, followed by etching and stripping of the resist, so as to form a circuit board. Meanwhile, in the plating method, copper is deposited in through holes by electroplating, and the through holes are then protected by solder plating, followed by stripping of a resist and etching, so as to form a circuit board.
In these methods, a photosensitive resin composition and a photosensitive element are used as the resist, and in particular, from the viewpoint of running costs and a working environment, an alkali developable resist is primarily used. Then, after the resist is cured, uncured portions are removed by an alkali developer, followed by rinsing by means of a spray pressure. Thus, a photosensitive resin composition to be used is required to have a tenting property which makes the composition unbreakable against the developer and the spray pressure used for rinsing, i.e., tent reliability. Further, in the plating method in particular, since a current density in a finely lined portion on a printed wiring board is higher than a current density in a loosely wired portion, plating in the finely lined portion becomes thicker than the resist, so that the resist in the portion is apt to be resist residue (resist residue due to overhanging). Hence, it is necessary that the resist does not remain after stripping even if the plating is overhung, that is, it have excellent stripping property.
In response to such requests, a photosensitive resin composition using a vinyl urethane compound and having good tent reliability is disclosed in Japanese Patent Application Laid-Open No. 271129/1993. However, such a photosensitive resin composition tends to have difficulty in conforming to increases in resolution which has been increasingly demanded year by year along with increases in density and precision of wiring of a printed wiring board. It is assumed that this is ascribable to a fact that an isocyanate residue having an urethane bond does not have excellent developability.
Further, an acrylate compound in which a polyethylene glycol chain solely exists is disclosed in Japanese Patent Application Laid-Open No. 232699/1993. However, when the polyethylene glycol chain exists alone, hydrophilicity is so strong that such problems as the deterioration of tent reliability or stripping property occur. Meanwhile, an acrylate compound in which a polypropylene glycol chain exists alone exhibits low resolution. Further, such an acrylate compound can be easily removed by an alkali developer. Hence, it causes the occurrence of sludge which is insoluble in the developer, and the sludge causes a short or a break when adhered to a substrate.
In addition to the foregoing requirements with respect to tent reliability and stripping property, it has also been necessary to shorten developing time for the purpose of improving the produceabillty of a printed wiring board. The present inventors have studied reduction in developing time in order to make a production process short. Heretofore, when a photosensitive resin composition layer having a thickness of about 37 to 42 μm is developed, development requires at least 25 seconds. However, if the developing time can be reduced to 20 seconds or less, the developing time is significantly reduced, and production time is in turn reduced. To reduce developing time, it is effective to improve the hydrophilicity of a binder polymer of the photosensitive resin composition However, an improvement in the hydrophilicity of the photosensitive resin composition lowers resistance to the developer, so that breakages of tents are liable to increase, in other words, tent reliability is liable to be lowered. For this reason, a photosensitive resin composition which achieves a reduction in developing time and has fully satisfactory tent reliability has heretofore not been available.